Contractor Forgot Washers
Contractor Forgot Washers
(OP)
Does anyone know of a code reference (AISC, UBC, IBC, etc..) that requires flat washers under the nuts of anchor bolts in tension.
The contractor forgot to install washers under the nuts that hold down a column base plate. Due to the forces on the structure, these bolts are in tension in a seismic event.
The bolts are 1 1/2" A36 threaded rod with nuts on both ends (1 end in concrete, 1 end above base plate). The hole in the plate is 1 5/8" diameter. The nuts are standard hex nuts.
As it stands, the nuts completely cover the hole in the base plate. However, I'm concerned with the hole distorting and possibly ripping the nut through the base plate.
The design force on the bolt is 50,000 lbs in a seismic event.
Any thoughts would be appreciated.
Thanks
The contractor forgot to install washers under the nuts that hold down a column base plate. Due to the forces on the structure, these bolts are in tension in a seismic event.
The bolts are 1 1/2" A36 threaded rod with nuts on both ends (1 end in concrete, 1 end above base plate). The hole in the plate is 1 5/8" diameter. The nuts are standard hex nuts.
As it stands, the nuts completely cover the hole in the base plate. However, I'm concerned with the hole distorting and possibly ripping the nut through the base plate.
The design force on the bolt is 50,000 lbs in a seismic event.
Any thoughts would be appreciated.
Thanks






RE: Contractor Forgot Washers
RE: Contractor Forgot Washers
It depends on what the base plate
material is. How do you know if he
used any in the concrete?
RE: Contractor Forgot Washers
The exercise will help concentrate the mind next time he is bolting down baseplates.
RE: Contractor Forgot Washers
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Contractor Forgot Washers
RE: Contractor Forgot Washers
I recommend you look at the standard specification language in the contract you use to see if it is in there.
RE: Contractor Forgot Washers
RE: Contractor Forgot Washers
In most jurisdictions, the EOR is responsible to verify any alteration to the anchorage system.
Dik
RE: Contractor Forgot Washers
RE: Contractor Forgot Washers
Dik
RE: Contractor Forgot Washers
I strongly recommend that you get a copy of the “Specification for Structural Joints Using ASTM A325 or A490 Bolts”. It can be found at this AISC link:
htt
Regards,
Lutfi
RE: Contractor Forgot Washers
Even if it works, make them do something. I think they should have to just put the washers in, as others have said.
RE: Contractor Forgot Washers
Anchor bolt washers are mentioned briefly in a couple places in AISC Steel Design Guide Series #1 "Column Base Plates", but no specific washer design recommendatons are given beyond using a heavy plate washer 5/16" to 1/2" thick when anchoring with oversize holes. In Table 14-2 of AISC steel Manual 13 th Ed., recommended washer sizes and thicknesses are given for various combinations of anchor rod diameters and baseplate oversize hole diameters.
Dumb question- Is your anchor design tension load of 50k a factored load? Allowable service load in tension for 1 1/2" dia a36 would only be 34k. Regards.
RE: Contractor Forgot Washers
RE: Contractor Forgot Washers
Dik
RE: Contractor Forgot Washers
RE: Contractor Forgot Washers
1. To protect the outer surface of the connected material from damage or galling as the bolt or nut was torqued or turned
2. To assist in maintaining a high clamping force in the bolt assembly
3 To provide surfaces of consistent hardness so that the variation in the torque-tension relationship could be minimized
4. Reduce the contact stress through increased surface area
5. Reduce stress risers form the discontinuity of the hole and bolt
6. To increase the bolt clamping surface area
7. To allow bolt shoulder to clear hole
It was not discussed what were the bolt type, the tightening method and connecting metal:
A325 bolts in general do not require the use of washers when using the turn of tun method. If a calibrated torque wrench is used, a washer should be used under the turned element, the nut or the bolt head. Washers are required under both the head and nut of A490 bolts when they are used to connect material with a yield point of less than 40 ksi. Also when bolts pass through a beam or channel flange that has a sloping interface, a bevel washer is often used to compensate for the lack of parallelism.
RE: Contractor Forgot Washers
A few answers:
The anchor bolt is 1 1/2" A36 threaded rod. The plate is also A36. The nuts or not pretensioned. The reason why is because they are anchor bolts for a steel tank which only go into tension in a seismic event.
The anchor load of 50k is the yield strength of the anchor. In steel tank design, the anchorage (base plate, concrete pullout, etc..) is designed for the anchor rod yield strength so the bolt will yield before the anchor attachments fail.
Thanks again for all the valuable input.